You can use the Context menu to find code, to find and replace certain found code, or to find and replace all found code.
Navigate to the page that has the desired JavaScript Editor, and right-click / control+click in the Editor.
On the Context menu, select Find/Replace.
On the Find/Replace dialog > Find text field, enter the code string you want to replace (in this case, $co) .
Note: If you are merely searching for all incidents of "$co" in the code, select the Find/Replace dialog's Find button > Close button. In the JS Editor, all incidents of the entered string are highlighted.
In the Replace with field, enter your replacement string (in this case, $c) .
Configure other search filters as desired, and, depending on the situation, select the Replace button (to replace only the first incident of the string) or the Replace All button (to replace all incidents of the string).
Note:Mirth® Connect performs the selected action and highlights the strings in the Editor.